This invention relates to a performance criteria in general, more particularly, to a system and method for automated process control of stages in articles manufacturing and most specifically to the integration of process control of separate manufacturing stages into a modular structure to yield a comprehensive goal oriented automated process control of the complete production line in a batch manufacturing process. This invention is also related to U.S. patent application Ser. No. 09/633,824 by Goldman, et al. entitled “Strategic Methods for Process Control” filed Aug. 7, 2000; to U.S. patent application Ser. No. 09/689,884 by Goldman, et al. entitled “System and Methods for Monitoring Process Quality Control” filed Oct. 13, 2000; and to U.S. patent application Ser. No. 09/731,978 by Goldman, et al. entitled “A Method and Tool for Data Mining in Automatic Decision Making Systems” filed Dec. 8, 2000, all of which are incorporated by reference for all purposes as if fully set forth herein.
Process control plays a fundamental role in attaining high yield of quality products. Among various process control methods, statistical process control (SPC) is well known. SPC relies on the observation of the deviation of a measurable process output parameter in the process from their statistically predicted distribution (e.g. by more than three standard deviations). SPC reveals trends towards a deterioration of a process as well as temporarily irregularities of parameters of a process.
All the aforementioned techniques suffer from inherent limitations resulting from the fact that their focus is the controlled variable, without linking the parameters, which influence the controlled variable. Thus, these techniques lack the ability to identify the combination of factors in a multi factorial process which is responsible for an observed deviation of an output of a process. Consequently, the process controlled by these methods can't be rectified on the fly, but rather can only be halted until the process engineer finds out the related problem.
To overcome this drawback, Goldman, et al in their patent application Ser. No. 09/689,884 entitled: “System and Method for Monitoring Process Quality Control” (hereinafter the POEM Application), described a method for an advanced process control (APC) which is essentially an on line monitoring and control of process parameters aimed to yield a robust process output having optimum statistical attributes (such as Cp and Cpk).
A modern production line comprises a great number of process stages performed in series by a diversity of manufacturing tools, thus a work piece which consist of an output of a first manufacturing tool is delivered as an input entity to a second manufacturing tool and so on until the product is finally shaped.
Furthermore, the term “manufacturing tool” represents a plurality of units performing the same process on various articles in parallel, e.g. a line of polishing machines in a microelectronic facility, each polishing one wafer at its time in accordance with the peculiar conditions of the machine, or a tool which can handle a plurality of items at once e.g. a diffusion oven which handles tens of wafers in a single run, or a plurality of inner units within a tool.
Until now, no quality control method did try to cope with the challenge that due to the “fact of life” that a production tool is not always tuned and therefore the designed nominal values of a process output carried out by this tool may vary within its tolerances in such a way that the final target will not be achieved. The present invention suggests a corrective action to be taken to “save” final target quality. This is achieved by a trade off mechanism which is based on a judicious combination of the deviating output with one or more other outputs which are deliberately diverted from their initially set target value.
Until now process control methods have been devised to control and optimize an output of a single stage in a multistage manufacturing process, and no attention was paid as to how the controlled parameters of a controlled first process affect an output of a subsequent second controlled process that follows (and functionally relies on the output of) the first stage. In addition, no attention was paid to the impact of subsequent stages output on previous stages outputs, with regard to the optimal values to be set as output targets.
The standard S88 defines hierarchical recipe management and process segmentation frameworks, which separate products from the processes that make them. The standard enables reuse and flexibility of equipment and software, and provides a structure for coordinating and integrating recipe-related information across the traditional ERP, MES, and control domains. S88 recipe control has a significant role in batch processes. Predictive control has been increasingly used in recent years in order to improve industrial processes including batch processes. There are some shortcomings to S88 that require improvement. Such improvements may lead to higher yields or higher average quality. FIG. 1 illustrates a S88 methodology in which three phases of a batch system are executed sequentially without any consideration for the results of other phases.
The S88 control recipe as it is implemented by using the SFC (or PFC) approach does not address data flow within inter-recipe execution. By looking at the SFC (or PFC) one can't tell which data item flows from where to where and what is its influence. Additionally S88 ignores inter recipe changes.
For example, the S88 does not have an in-built solution to compensate for deviations such as when at the end of a certain phase the temperature of the material is different then the target temperature. When this happens most users ignore such changes. The most popular way of dealing with changes is the golden batch approach: aping a process that leads to production of a serendipitously ideal batch.
As a result it is nowadays very difficult to have a global process control, which integrally combines all the various steps in a processes. The present invention fulfills this gap and provides other related advantages as is detailed below.